Components of thermostatic units and laser welding method for producing the components

ABSTRACT

A method for joining components of thermostatic systems and thermal relays for low-voltage circuit breakers, the components being constituted by at least one bimetallic element constituted by a lamina with a first face and a second face and at least one connection element that has a substantially flat end part with a third face and a fourth face, its particularity consisting of the fact that it comprises the steps that consist in:—overlapping and coupling the end part of the first face of the bimetallic element with respect to the third face of the end part of the connection element;—subjecting the end part of the second face of the bimetallic element to the welding action of laser means to provide a weld between the bimetallic element and the connection element.

BACKGROUND

The present invention relates to components for thermostatic units (ofthe kind used in thermostatic systems with a bimetallic element forenvironments or technical systems or in thermal protection relays forlow-voltage circuit breakers), particularly to bimetallic elements andtheir connections to other components of said thermostatic units, and toa method for producing them. In particular, the present inventionrelates to a method for joining the bimetallic elements to othercomponents of the thermostatic units by means of a laser weldingprocess.

In low-voltage circuit breakers in the current art, the bimetallicelement can generally be joined to the other components of thermostaticunits, for example braids or terminal connection elements of athermostat or the moving contacts of a circuit breaker, by mechanicalcoupling or by braze welding.

The mechanical joining of said bimetallic elements is performedtraditionally by using rivets, nails, pressure-based systems or similarjoining systems. Although this method provides an efficient joiningsystem, it has drawbacks. In particular, electrical conductivityproximate to the contact points is not ideal and can vary among parts.Furthermore, the mechanical joining operation still requires a largernumber of parts (for example rivets or nails) than strictly required forthe functionality of the thermostatic unit, thus introducingcomplications in the assembly process and entailing in any case anincrease in production costs.

As an alternative to mechanical coupling, the bimetallic element and theother components of the thermostatic units can be joined by virtue ofconventional braze welding processes. These methods do not entail thedrawbacks noted above, but entail other different ones, linked to theconsiderable application of heat required by this technology. As isknown, the application of heat is a critical element in the welding ofbimetallic elements, since it can entail structural variations of saidbimetallic element. Accordingly, its performance is reduced, andtherefore the number of substandard parts increases and in any case thebehavior is uneven among parts.

It is evident, from what has been described above, that the current artneeds to have components of thermostatic units that have a uniformbehavior and can be manufactured efficiently. It is also evident thatthe current art needs to have an efficient method for joining componentsof thermostatic systems and thermal relays for low-voltage circuitbreakers and particularly for joining bimetallic elements to the othercomponents of the corresponding thermostatic units.

The aim of the present invention is to provide components ofthermostatic units that can be manufactured efficiently and have auniform behavior.

SUMMARY

Within the scope of this aim, an object of the present invention is toprovide a method for joining components of thermostatic units, andparticularly bimetallic elements to the other components of thermostaticsystems and thermal relays for low-voltage circuit breakers that doesnot entail metallic joining systems.

Another object of the present invention is to provide a method forjoining components of thermostatic units and particularly bimetallicelements to the other components of thermostatic systems and thermalrelays for low-voltage circuit breakers that does not entail scarcelycontrollable heat application systems.

Another object of the present invention is to provide a method forjoining components of thermostatic units and particularly bimetallicelements to the other components of thermostatic systems and thermalrelays for low-voltage circuit breakers that does not determinestructural variations in said bimetallic element.

Another object of the present invention is to provide a method forjoining components of thermostatic systems and thermal relays forlow-voltage circuit breakers and particularly bimetallic elements to theother components of thermostatic systems and thermal relays forlow-voltage circuit breakers that ensures mass reproducibility.

Another object of the present invention is to provide a method forjoining components of thermostatic systems and thermal relays forlow-voltage circuit breakers and particularly bimetallic elements to theother components of thermostatic systems and thermal relays forlow-voltage circuit breakers that has a modest cost and is economicallycompetitive.

This aim, these objects and others that will become better apparenthereinafter are achieved by means of a method for joining components ofthermostatic units, said components being constituted by at least onebimetallic element constituted by a lamina with a first face and asecond face and at least one connection element that has a substantiallyflat end part with a third face and a fourth face, characterized in thatit comprises the steps that consist in:

-   -   overlapping and coupling the end part of the first face of said        bimetallic element with respect to the third face of the end        part of said connection element;    -   subjecting the end part of the second face of said bimetallic        element to the welding action of laser means to provide a weld        between said bimetallic element and said connection element.

It has been found in fact that by using a laser welding system and byworking on one face of the bimetallic element according to the method ofthe present invention, a joint is provided between the bimetallicelement and the connection element that does not have the drawbacks ofthe known art, since the mechanical coupling means are avoided and thereis no application of heat that is critical for the bimetallic element.

Further characteristics and advantages of the method according to thepresent invention will become better apparent hereinafter with referenceto the description given hereafter and to the accompanying drawings,given merely by way of non-limiting examples and wherein the onlyfigures are schematic views of a system for welding components ofthermostatic units provided according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a system for welding components ofthermostatic units according to one embodiment.

FIG. 2 is a schematic view of a system for welding components ofthermostatic units according to another embodiment.

DETAILED DESCRIPTION

In the accompanying FIG 1, the bimetallic element is designated by thereference numeral 1. Said element is constituted by a lamina with afirst face 10 and a second face 20. A connection element, for examplethe connection of a thermostatic system or relay, is designated by thereference numeral 2. The connection element 2 has a flat end part with athird face 30 and a fourth face 40. The end part of the first face 10 ofthe bimetallic element is superimposed and coupled to the third face 30of the end part of the connection element. The end part of the secondface 20 of the bimetallic element is subjected to the welding action oflaser means 50, so as to provide a weld between the bimetallic elementand the said connection element.

Preferably, in the method according to the invention the laser weld isnot a spot weld but a continuous weld. For this purpose, the laser means50 scan the second face 20 of the bimetallic element according to apredefined path. It is evident to the person skilled in the art thatsaid scan can be performed by virtue of a relative movement of the lasermeans with respect to the components to be welded during the weldingoperation. In practice, said relative movement can be performed bykeeping the components to be welded motionless and moving the lasermeans, or by keeping the laser means motionless and moving thecomponents to be welded, or by moving both.

Preferably, said scan according to a preset path follows a curvedprofile, as shown in the figure. As an alternative, however, it ispossible to perform said scan along mixed and even discontinuous brokenlines (curved and straight portions). Said lines can also be replicatedin multiple regions of the face to be welded for example in asubstantially parallel manner.

The speed, power, angle of incidence, frequency, amplitude and otherphysical characteristics of the scanning beam can be chosen andmodulated according to the characteristics of the elements to be welded,such as for example their chemical nature or their thickness.

Although it is possible to use laser means of a different type, it ishighly preferable to use a solid-state laser, for example a Nd-crystallaser. In this case also, the characteristics of use of the laser, suchas for example the frequency, power and angle of incidence, can bechosen and modulated as a function of the characteristics of theelements to be welded and of the results to be obtained.

It has been found in practice that by using the method according to theinvention it is possible to weld the bimetallic element to variouscomponents of thermostatic systems and thermal relays for low-voltagecircuit breakers. In particular, it has been found that it is possibleto weld the bimetallic element to rigid connections and also toconnecting braids.

In this last case, the end part of the connecting braids must bemachined and shaped appropriately so as to allow coupling to one face ofthe bimetallic element and its welding thereto. FIG. 2 (in whichreference numerals repeated from FIG. 1 indicate similar features),illustrates an embodiment in which a connection element 2 a is aconnecting braid.

The method according to the invention solves the problems of the knownart and has many advantages over it.

In particular, it is not necessary to use mechanical connectingelements, thus reducing the number of parts to those strictly necessaryfor the functionality of the circuit breaker. The assembly operations,moreover, are simplified, consequently saving on production times andcosts.

Moreover, the use of laser means allows to avoid applications of heatthat would be critical and damaging for the bimetallic element. Ingeneral, the efficiency and reproducibility from part to part of themethod according to the invention are greater than those of the methodsof the known art, thus reducing the number of rejects and substandardparts and increasing the overall economy of the production process.

With the method according to the invention it is therefore possible toobtain components of thermostatic systems and thermal relays forlow-voltage circuit breakers that have improved characteristics withrespect to the components of the known art. These components, like thedevices (for example circuit breakers) that comprise them, constitute anadditional aspect of the present invention.

In practice it has been found that the method according to the inventionand the components of low-voltage circuit breakers obtained therewithfully achieve the intended aim and objects. The method thus conceived issusceptible of numerous modifications and variations.

All the details may furthermore be replaced with other technicallyequivalent elements.

1. A method for joining components of thermostatic systems and thermalrelays for low-voltage circuit breakers, said components beingconstituted by at least one bimetallic element constituted by a laminawith a first face and a second face and at least one connection elementcomprising a connecting braid that has a substantially flat end partwith a third face and a fourth face, wherein the method comprises:overlapping and coupling the end part of the first face of saidbimetallic element with respect to the third face of the end part ofsaid connection element; and subjecting the end part of the second faceof said bimetallic element to the welding action of laser means toprovide a weld between said bimetallic element and said at least oneconnection element, wherein: said laser means scan the second face alonga predefined path that follows a curved profile; and said curved profileis designed entirely within said second face and has no intersectingportions.
 2. The method for joining components of low-voltage circuitbreakers according to claim 1, wherein said laser means are constitutedby a solid-state laser.
 3. The method for joining components oflow-voltage circuit breakers according to claim 2, wherein the at leastone connection element comprises a circuit breaker protection relayconnection.
 4. The method for joining components of low-voltage circuitbreakers according to claim 1, wherein the at least one connectionelement comprises a circuit breaker protection relay connection. 5.Components of low-voltage circuit breakers obtained with a methodaccording to claim
 1. 6. A low-voltage circuit breaker, comprising oneor more components according to claim 5.